1. Field of the Invention
The present invention relates to a circuit for speeding up a read operation from a ROM from which program data is read by a control device such as a microcomputer and the like.
2. Prior Art
Microcomputers generally decode program data read from a ROM and execute various logical operations in conformity with the decoded program data. Programs stored in a ROM include varieties of instructions, say, those from a one-byte instruction where one instruction is executable only by decoding program data at each address to a plurality-of-bytes instruction where one instruction is executable by sequentially decoding program data at a plurality of addresses.
Such a microcomputer increments the counts of a program counter, and thereafter accesses ROM for each address. Accordingly, the one-byte instruction is executed by accessing an address in the ROM once, while the plural bytes instruction are executed by sequentially accessing a plurality of addresses in the ROM.